Recent improvements in their spatial and data resolution capability have made digital image processing systems particularly attractive for multi-use environments, in which the user has the option of selecting the type of reproduction device and the desired resolution of the reproduction device. In still color image photography, for example, when an image, that has been captured on color photographic film or a high spatial resolution color digital camera, is digitized and stored in an attendant data base, it can be readily optimized for reproduction on a variety of output devices (e.g. a color video display or a digitally driven, high resolution color thermal printer) through the use of workstation-resident image processing software.
One example of a digitized image processing system that takes advantage of this capability is the color photo-finishing system disclosed in co-pending patent application Ser. No. 582,305, filed Sep. 14, 1990, by S. Kristy entitled "Multi-resolution Digital Imagery Photofinishing System," assigned to the assignee of the present application and the disclosure of which is herein incorporated. As explained in that application, conventional photo-finishing of consumer-generated still color photographs (e.g. those captured on 35 mm color film) customarily involves the use of an analog electro-optic system and an associated chemical-based print developing unit. The Kristy application describes a digital image-based photofinishing apparatus that enables the user to personally customize and obtain high quality prints of photographic images. It also provides for the storage and retrieval of high spatial resolution digitized color still images for playback to a variety of reproduction devices, the spatial resolution of which may vary.
FIG. 1 diagrammatically illustrates such an improved photofinishing apparatus as employing a high spatial resolution opto-electronic film scanner 12, the output of which is coupled to a host digitized image processor 14. By high spatial resolution is meant a pixel array of a size and density sufficient to provide color print quality images normally provided by analog optical systems. Scanner 12 may comprise a commercially available Eikonix Model 1435 high spatial resolution scanner, having a very high spatial resolution sensor pixel array (a 3072.times.2048 pixel matrix) capable of generating high spatial density-representative output signals which, when converted into digital format, yield `digitized` photographic image files from which high quality color prints may be obtained. Scanner 12 is arranged to be optically coupled with a photographic recording medium, such as a consumer-supplied 35 mm color film strip 16. Film strip 16 typically contains a plurality (e.g. a set of twenty-four or thirty-six) 36 mm .times.24 mm color image frames. For each scanned image frame, scanner 12 outputs digitally encoded data, representative of the opto-electronic response of its high resolution imaging sensor pixel array, onto which a respective photographic image frame of film strip 16 is projected by the scanner's input lens system.
This digitally encoded data, or `digitized` image, is supplied to host processor 14 in the form of an imaging pixel array-representative bit map, resolved to a prescribed digital code width (e.g. eight bits per color per pixel). Host processor 14 has a resident image-encoding and storage operator through which each high spatial resolution digitized image file may be stored in a multi-resolution, hierarchical format. The use of such a multi-resolution, hierarchical storage format facilitates retrieval of images for reproduction by a variety of devices the resolution of which may vary from device to device, such as a low/moderate NTSC television monitor or a very high resolution, digitally driven, color thermal printer.
One example of a preferred encoding and storage operator that may be used for this purpose is described in U.S. Pat. No. 4,969,204, issued Nov. 6, 1990, entitled "A Hybrid Residual-Based Hierarchical Storage and Display Method for High Resolution Digital Images in a Multi-use Environment," by Paul W. Melynchuck et al, assigned to the assignee of the present application and the disclosure of which is herein incorporated. As described in the Melynchuck et al application, an original high spatial resolution (2048.times.3072) image may be sequentially decomposed into a hierarchical set of respectively different resolution residual images plus a base resolution image file. The base resolution file may comprise a 512.times.768 pixel array file formatted as a set of four interlaced (256 lines by 384 pixels/line) lowest resolution image sub-arrays, respectively corresponding to odd pixel/odd line, odd pixel/even line, even pixel/odd line, even pixel/even line sub-arrays. One of the lowest resolution image (256.times.384) sub-arrays is suitable for preliminary display on an NTSC-quality video monitor, while the full 512.times.768 base resolution array provides a high quality image on a an NTSC video monitor. An individual lowest resolution 256.times.384 sub-array may be further sub-sampled to obtain one or more lower resolution files (e.g. a 128.times.192 pixel sub-array) for supporting the display of one or more relatively smaller images. The spatial parameters of each of the hierarchical image files into which an original (2048.times.3072) digitized image file is encoded and stored are chosen to facilitate the implementation and incorporation of a low cost, reduced complexity frame store/data retrieval architecture into a variety of reproduction devices, thereby providing for rapid call-up and output (display or print out) of one or more selected images.
Now, although a multi-resolution, multi-use system, such as described in the above-referenced Kristy application, affords rapid access to a variety of image formats and allows the user to select the reproduction medium and the spatial resolution at which the accessed image is reproduced, there still remains the problem of adjusting the parameters of the digitized image file in the event that a change in metric, for example a change in color metric, is required.
More specifically, with the ability of a multi-resolution, multi-use imaging storage and retrieval mechanism to drive a wide variety of output devices, it can be expected that the metric of a chosen output device may not necessarily match that of a selected image stored in the multi-resolution data base. Consequently, before imagery data to be accessed from the hierarchical data base is supplied to a selected output device, it must undergo a metric conversion. One way to adjust the image is to install a metric conversion operator between the data base and the output device. However, depending upon the complexity of the metric conversion required and the spatial resolution of the output device, the computational intensity of the metric conversion operator can become quite significant in terms of processing overhead.
In this context, it is observed that a metric change may involve anything from a single channel independent modification to a series of multi-channel color space transformations. Although a low level metric change may not require a significant amount of additional image processing, executing a more intense metric change in a very high spatial resolution application, such as in the case of a 2040.times.3072 pixel array thermal printer, can be particularly computationally intensive.